JDK-8165443 : Free Collection Set serial phase takes very long on large heaps
- Type: Enhancement
- Component: hotspot
- Sub-Component: gc
- Affected Version: 9
- Priority: P3
- Status: Resolved
- Resolution: Fixed
- Submitted: 2016-09-05
- Updated: 2025-08-07
- Resolved: 2019-12-09
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| JDK 14 |
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14 b27Fixed  |
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Description
Even after fixing JDK-8165313, a significant amount of time is spent in the Free Collection Set Serial part of the GC.
E.g. with -Xmx20g -Xms20g -XX:NewSizePercent=65 -XX:MaxNewSizePercent=80 -XX:G1RegionSize=1m on gcbasher, time spent in that phase is still in the range of 20ms (instead of >100ms) with ~14k regions.
Running with analyzer enabled, the work distribution is kind of this (accumulated times of a single run in ms):
G1SerialFreeCollectionSetClosure::doHeapRegion: 107
G1CollectedHeap::free_region 38
TruncatedSeq::add(double) 18
SurvRateGroup::record_surviving_words 9
G1COntiguousSpace::used 2
(I kind of think that the TruncatedSeq::add() measurements were part of SurvRateGroup::record_surviving_words(), but somehow did not get attributed correctly)
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